In communications systems, duplexers provide the ability to receive and transmit signals while using the same antenna. In a typical transmission operation, only signals of a designated transmission frequency are passed to an antenna, which transmits the signal as a radio signal into the air. In a typical receiving operation, a signal received by an antenna is transmitted to the duplexer to select only a signal of the designated frequency. A duplexer uses resonant circuits to isolate a transmitter from a receiver for allowing the transmitter and the receiver to operate on the same antenna at the same time without the transmitter adversely affecting the receiver. Duplexers use filters, such as various pass band filters and notches to accomplish isolation and continuity in signal transfer. In duplexer operation, filters must pass the desired signal while rejecting as much as possible of the undesired signals.
The increased diversity in the functionality of mobile phones has resulted in an increase in the complexity of duplexer design. For example, increased mobile phone functions such as dual mode (e.g., a combination of an analog mode and a digital mode, or a combination of digital modes, such as TDMA or CDMA), and a dual band (e.g., a combination of an 800 MHz band and a 1.9 GHz band, or a combination of a 900 MHz band and a 1.8 GHz band or a 1.5 GHz band) have been increasing the complexity of mobile phone architecture and circuitry. Increased implementation of frequency related functions affect antenna bandwidth. Antenna bandwidth is generally the range of frequencies over which the antenna can operate while some other characteristic remains in a given range. Therefore, increased frequency ranges increase demand for performance over a number of frequency channels, or a wide bandwidth antenna. Moreover, to support these multiple, diverse functions while maintaining proper isolation and reliable signal transfer between transmitter and receiver operations, present communication devices use fixed, redundant circuitry, such as an increased quantity of switches and filters to compensate and broaden duplexer capabilities. Accordingly, such increased use and quantity of filters creates the need for optimizing filter performance.
There is a continuing demand for component reduction and high performance communications devices. Elimination of redundant components, functions, or circuitry is highly desired in communication electronics. Increased performance in communication devices without increasing device size or weight is similarly desirable. Further, there is a continuing need for reliable and quality signal transfer, improved transmitter-receiver isolation, and very high Q value circuitry with respect to duplexers. In addition, further considerations include polarization, tradeoffs between isolation and size, tuning precision, and transmit/receive frequency spacing for a given band versus wholesale tuning between bands.
Micro-electro-mechanical system (MEMS) technology is currently implemented for various filtering circuitry. Exemplary MEMS components that have been used for filtering include MEMS capacitors and acoustic resonators. Although there have been improvements in the development of MEMS components for filtering, there is a continuing need for improved performance and stability of these components as well as tunability for optimal performance and multi-band applications.
Therefore, room for improvement exists for improved duplexer circuitry and related components and improved MEMS components for use in duplexer circuitry.